1. Field of the Invention
The subject invention generally pertains to what is known as a horizontally sliding door and more specifically to a retention system for such a door.
2. Description of Related Art
So-called horizontally sliding doors (which may actually slide or roll) usually include one or more door panels that are suspended by carriages that travel along an overhead track. The carriages allow the door panels to slide or roll in a generally horizontal direction in front of a doorway to open and close the door. The movement of the panels can be powered or manually operated. Depending on the width of the doorway and the space along either side of it, a sliding door can assume a variety of configurations.
For a relatively narrow doorway with adequate space alongside to receive an opening door panel, a single panel is enough to cover the doorway. Wider doorways with limited side space may require a bi-parting sliding door that includes at least two panels, each moving in opposite directions from either side of the doorway and meeting at the center of the doorway to close the door. For even wider doorways or those with even less side space, multi-panel sliding doors can be used. Multi-panel doors have at least two parallel door panels that overlay each other at one side of the doorway when the door is open. To close the door, one panel slides out from behind the other as both panels move in front of the doorway to cover a span of about twice the width of a single panel. Applying such an arrangement to both sides of the doorway provides a bi-parting door with multiple panels on each side.
Although sliding doors are used in a wide variety of applications, they are particularly useful in providing access to cold-storage lockers, which are rooms that provide large-scale refrigerated storage for the food industry. Doorways into such a room are often rather wide to allow forklift trucks to quickly move large quantities of products in and out of the room. When closing off a refrigerated room, sliding doors are often preferred over roll-up doors and bi-fold doors, because sliding panels can be made relatively thick with insulation to reduce the cooling load on the room.
Thicker panels generally provide better thermal insulation, and a panel's rigidity allows the panel to compress seals against gaskets mounted to the stationary structure surrounding the door. Alternatively, the panel itself may carry compressive seals, and the rigidity allows the panel to accurately position its seals and allows the door panel to transmit (in a direction generally coplanar with the panel) the necessary compressive forces required to tightly engage the seals. Unfortunately, a relatively thick, rigid door does create some problems, especially in cold-storage applications.
With cold-storage rooms, it is important to open and close the door as quickly as possible to minimize the room's cooling load. So, the doors are usually power-actuated, and they are opened and closed automatically in response to sensing the presence of an approaching vehicle, such as a forklift. Although power-actuated, vehicle-sensing systems are effective, occasional collisions between a forklift and a door panel may still occur. If the door panel is relatively thick and rigid, as is the case with typical cold-storage doors, a collision may damage the door panel or other parts of the door.
Damage to a door may be avoided by providing the door with some type of breakaway feature that releases the door panel upon impact. This is easily accomplished with roll-up doors and overhead storing doors (e.g., conventional garage doors) where the door panels or curtain moves vertically between two parallel tracks. The breakaway feature is simply incorporated in the area where the vertical side edges of the door panel travels within its respective vertical track.
Applying a breakaway feature to a horizontally sliding door of a cold storage room, however, is much more complicated because such door panels not only move horizontally, but they may also have some vertical movement to engage the door's lower seal as the door panel comes to its closed position. And a horizontally sliding door may not even have a lower track. The location to mount breakaway hardware is more limited with horizontally sliding doors because the floor underneath the door panel is preferably kept clear of door-related hardware. Floor-mounted hardware can create a tripping hazard and may itself become damaged by vehicles traveling near the doorway.
Nonetheless, some sliding doors do have floor-mounted hardware, such as those disclosed in U.S. Pat. Nos. 4,404,770; 3,611,637 and 4,651,469. The '637 patent has a lower track, but the track apparently is not intended to provide a breakaway function. The same appears to be true for the '770 patent. For the '469 patent, at first glance FIG. 10 makes the door panel appear as though it can breakaway; however, there is no indication that the lower edge of the door panel can actually get past its floor-mounted guide.
Another more interesting sliding door is disclosed in U.S. Pat. No. 6,330,763. This patent discloses how a wall-mounted nylon strap can be used for restraining the lower portion of a door panel. The pliability of the strap enables the door panel to yield under impact and automatically return to its normal position. The strap, being of limited length, effectively tethers the door panel to limit how far the door panel can be displaced, and the slackness or pliability of the strap provides the door panel the freedom to return on its own; however, the nylon strap does not necessarily have the resilience to forcibly draw the panel back into position.